V8, 2 stroke poppet valve Lexus 1UZ engine 1

[Letlhakane]

Has any one got any experiance with two stroke poppet valve engines that they would like to share. I have built a Lexus 1uz V8 which is running as a two stroke. This project is primerily for increasing the volumetric efficiency for racing purposes. Any comments will be apreciated.

 

[gruntguru]

Good point bradrs. I will add that although total voltage output of the coil needs to be almost double the requirement for "waste spark" operation, insulation should not be a problem. Although coil output voltage is almost double, one plug sees positive voltage and the other negative. Therefore each HT lead will only see the voltage level it sees when "firing" a plug in waste spark mode.

je suis charlie

 

[bradrs]

I agree gruntguru, the HT should be OK. I was more concerned with the windings in the secondary(output side) of the coil. They will be producing potentially close to double the voltage. And depending on how the coil windings are done, that could be a problem. It could increase the voltage between neighboring turns in the coil, making it easier to burn through coating or epoxy. A split bobbin which divides the windings into sections helps with that, but you'd probably need to slice a coil to see if that is the case. I'd just call it something to keep in mind, if you run into ignition issues.

 

[RodRico]

I watched the video at [URL unfurl="true"]https://www.facebook.com/ian.crawford.100/videos/588699737919534/[/url] . Very cool.

Ian, come join us on Facebook at

https://www.facebook.com/groups/757021827686019/

!

 

[RodRico]

Letlhakane, I shared your video in the "All sorts of multi cylinder engines" group on Facebook, and a sharp viewer noticed the video is sped up during the reving sequences by watching your hand at the end of the clip. Is he right?

 

[enginesrus]

It looks sped up. Has it been on a dynamometer yet? I guess it has a strange sort of loop charging effect, I always wanted to try that, sure would like to see how the HP compares to the 4 stroke version.

 

[gruntguru]

Just ocurred to me that the chamber design could be usefully improved in line with the needs of a two stroke.

Firstly - typical pent-roof tumble works against you here. The first thing encountered by much of the intake flow is - the open exhaust valves - short circuiting the scavenge process. Reverse tumble would be preferrable - perhaps a wide valve angle with vertical intake port between the valves.

Secondly - the valves are always closed at TDC so the piston crown can be fitted much closer to the valves (no valve reliefs) with a small chamber concentrated around the spark plug.

je suis charlie

 

[Letlhakane]

In reply to rodrico's statement about a sharp observer noticing some thing untoward about the video clip I can only say this: I took the video my self with a Nokia N8 phone in one hand and operating the engine with the other. The video has not been edited,tampered with or otherwise modified in any way, it was simply downloaded from the phone then uploaded to FB from there it was downloaded and uploaded to this forum.

 

[BrianPetersen]

Doesn't look sped up to me, just quick hand motions. This engine is going to sound like it is spinning faster than it is. Each exhaust manifold will have 4 pulses per revolution discharged from it, evenly-spaced on each bank. It won't have the once-every-two-revolutions superimposed frequency that a normal 4-stroke V8 has because of its irregular firing pattern into each exhaust manifold. No "V8 rumble".

Detroit Diesels were nicknamed "screaming Jimmy" for much the same reason. They sound like they're spinning much faster than they actually are.

 

[RodRico]

In reply to rodrico's statement about a sharp observer noticing some thing untoward about the video clip I can only say this: I took the video my self with a Nokia N8 phone in one hand and operating the engine with the other. The video has not been edited, tampered with or otherwise modified in any way, it was simply downloaded from the phone then uploaded to FB from there it was downloaded and uploaded to this forum.

I meant no offense. I was simply reporting what many said and asked you to clarify one way or the other.
I told folks I didn't think it was sped up, but then someone pointed out the very last 7 seconds where your hand seems to move abnormally fast, and I became less sure.

The video of your engine I posted in the "All sorts of multi cylinder engines." group on Facebook now has 258 comments (many are repetitious because folks don't read all the prior comments before asking a question). Most comments are simple statements of awe. A surprising number are people saying "it can't be a two stroke because it has valves." Others have disabused them of the notion. You really should join the group!

 

[enginesrus]

How about the HP figures? Power and torque curves?

 

[Letlhakane]

There are no HP or torque figures available as I live in Botswana and as far as I am aware there are no dyno's available here. I would need to take it to South Africa to do this but realisticaly it would be much simpler to test it on a drag strip (also in South Africa)after this current Covid story is sorted.
The quick hand action, at the end of the video, clearly indicates how responsive the engine is and the possibility of over reving is very real.
bradrs has commented on the ignition system and it seems that he is far ahead of me on this subject. Originaly the engine had two coils and two distributers The distributers simply distributed the HT current to the varios cylinders, nothing else. Now I have installed four dual coils fired by four triggers and removed the distributers. The thinking was that this should be the same, or similar, as having eight coils. Would it be a better solution to go the "coil on plug" route?
gruntguru is suggesting that some of the fresh scavenging air is short circuited and passes out through the open exhaust valves. This is certainly correct and I am using a 6-71 blower instead something larger. The 6-71 blower is sufficient to charge a 7 liter (427CU) Detroit at 6 PSI with the blower spinning at crank X 2 so the thinking here was that this setup may be a "bit light on" with the blower turning at crank + 20% on a 4 liter engine. Having the inlet valves/ports in a more vertical possition would be beneficial but not possible for me to accomplish. Non rotating inlet valves with shrouds on the stem side facing the exhaust valves could also be a practical solution.
RodRico, I am waiting for a response for approval from "All sorts of multi cylinder engines" Thanks to you all for the suggestions!

 

[Lou Scannon]

Maybe you've thought of this already: I see no need for a massive (e.g. stock) flywheel. You could probably get away with the lightest possible piece that can take the torque transfer to the clutch.
But, caution, considering the rpm you will reach - make sure whatever you use has the needed integrity.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Letlhakane]

Lou, it will be using a stock torque converter

 

[Lou Scannon]

I see.
Not my area of expertise, but is a stock converter well adapted for racing use? Coming to mind are items such as stall speed, torque capacity, and rpm capability.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[TugboatEng]

7500 rpm isn't significantly over the base engine's normal speed range.

Stall speed is a function of torque and converter diameter. Advertised stall speeds are an estimate based on a lot of assumptions. This engine will likely have close to double the stall speed with the stock conveetrt.

 

[gruntguru]

gruntguru is suggesting that some of the fresh scavenging air is short circuited and passes out through the open exhaust valves. This is certainly correct and I am using a 6-71 blower instead something larger. The 6-71 blower is sufficient to charge a 7 liter (427CU) Detroit at 6 PSI with the blower spinning at crank X 2 so the thinking here was that this setup may be a "bit light on" with the blower turning at crank + 20% on a 4 liter engine. Having the inlet valves/ports in a more vertical possition would be beneficial but not possible for me to accomplish. Non rotating inlet valves with shrouds on the stem side facing the exhaust valves could also be a practical solution.

I think a deflector welded into the combustion chamber would be better. Perhaps recess the exhaust valves into the head a little and add a "mound" around the perimeter nearest the intake valves.

je suis charlie

 

[Letlhakane]

I like the idea of the welded in deflector as this can be customized in all possible ways to achieve the desired result without the risk of something breaking or falling off into the works. I will need to look for a set of heads to play with.

 

[RodRico]

I like the idea of the welded in deflector as this can be customized in all possible ways to achieve the desired result without the risk of something breaking or falling off into the works. I will need to look for a set of heads to play with.

You may not even have a significant problem. You're scavenging for a whopping 50 degrees then pressurizing the intake for 65 degrees and presumably firing the injectors shortly after exhaust closes, so you shouldn't have any direct transfer of fuel out the exhaust. That leaves spoiling of combustion due to excess EGR which is manifest as unburnt hydrocarbons in the exhaust (see

https://x-engineer.org/automotive-e...ecirculation-egr-complete-guide-introduction/

). Here in the US we can get a reading on unburnt hydrocarbons at any emissions test site. Do you have emissions test facilities in Botswana, perhaps in the largest city? As long as you don't have excess oxygen or unburnt hydrocarbons in the exhaust, I believe you're getting maximum power out of your engine given the available airflow and compression ratio.

 

[Letlhakane]

To be true full, I really don't know if there are any regulations here regarding motor vehicle emissions. Basically it seems if it runs okay, its good. So there is no testing of light motor vehicles after they have been first registered. Even when the car is secondhand and imported when they are first registered there are no emissions tests done .

 

[RodRico]

O2 sensors are easy enough to obtain. I wonder whether there's such a thing as a small unburnt hydrocarbon sensor.